Abstract

Endometrial carcinoma (EC) harboring POLE exonuclease domain mutations occurs in 5-15% of ECs and frequently affects young women with low body mass index (BMI). It presents at early stage as high grade endometrioid histotype with intense tumor infiltrating lymphocytes and has good clinical outcomes and favorable prognosis. In this article we report the case of a 32-year-old woman with endometriod EC (EEC) exhibiting a “ultramu- tated” molecular profile and an excellent prognosis despite tumor size and grading. Herein, to highlight the importance of defining POLE status in ECs for both clinical and therapeutic implications for patients.

Introduction

Endometrial carcinoma (EC) is the fourth most common tumor affecting women and represents the second most common gynecologic malignancy ^1,2.

The historical ECs pathogenetic classification has been improved by molecular classification, in subgroups described by The Cancer Genome Atlas (TCGA) Research Network ³. In 2015, Talhouk et al., proposed for the first time a clinically applicable molecular-based classification for endometrial cancers ¹ highlighting the importance of clinical and pathological analysis for better patient management.

Among molecular subtypes, POLEmut EC, which accounts for less than 10% of all ECs, are typically indolent, presenting at low stage in younger women with lower BMI, frequently exhibiting high grade endometrioid-phenotype and intense tumor-infiltrating lymphocytes ^1,2,4.

Case report

We report the case of a young woman, aged 32 years, who presented with intermenstrual abnormal uterine bleeding and an endometrial lesion was identified at colposcopy, and so biopsies were performed. Bioptic material was fixed in formalin and imbedded in paraffin for histopathological examination. We observed a solid and glandular proliferation characterized by both evident architectural and cytological atypia. We diagnosed these findings as endometrial endometrioid carcinoma grade 3 FIGO (Figs. 1-2).

The patient underwent MRI that showed an abnormal dishomogeneous formation arising from endometrial cavity. The tumor was 7 cm in its maximum diameter and filled the entire uterine cavity extending to the cervix (1B FIGO radiological staging).

New biopsies were performed for immunohistochemical analysis and we detected an elevated proliferative index by Ki-67 and a heterogeneous immunoreaction for p53 (Fig. 3).

MSI status by immunohistochemical studies was analyzed and no microsatellite instability was observed.

Tumor DNA extracted from paraffin samples has been completely sequenced through Next-Generation Sequencing (NGS), showing a large number of sequence alterations (Tab. I) and an average read depth in analyzable target regions equal to 1042. Coverage data and allelic frequency showed a minimal coverage level equal to 782 and a minimal allelic frequency equal to 12%, indicating an optimal sequencing performance.

The major pathogenetic mutations reported on database and on prediction sites were referred to POLE (Pro286Arg and Asn1396Ser), MSH6, BRCA1 and PTEN (Tab. II).

Discussion

Endometrial carcinoma is the most frequent tumor affecting women in the developed countries and represents the second most common malignant tumor in female patients ^1,2.

Since TCGA proposed the current subgroup classification, the integration of clinical, morphological and molecular data has been highlighted by many authors, focusing attention on MSI, TP53 and POLE status and recognizing four molecular subgroups with specific therapies and prognosis ³:

1. “ultramutated” tumors harboring pathogenic POLE mutations;
2. “hypermutated” tumors, characterized by mismatch repair deficiency (MMRd);
3. “NSMP” (no specific molecular profile), low copy number (p53 wild-type);
4. “high copy number” (abnormal p53) ³.

In 2015, Talhouk et al. proposed, a diagnostic algorithm based on a limited panel of immunohistochemistry (MMR proteins and p53 expression) and POLE mutation analyses¹.

Distinguishing the EC molecular subgroups has clinical and prognostic implications: a woman, often younger as compared to average age at diagnosis, usually presenting at early stage with high grade EC harboring pathogenic POLE mutation, benefits from conservative treatment and has an excellent prognosis ^1,3,4.

POLE is the acronym for polymerase epsilon, a protein with a catalytic subunit responsible for DNA replication and repair mechanisms. POLE alterations are bounded with neoplastic transformation due to an acquired “ultramutated” phenotype (232 x10^-6 mutations per Mb), not only in ECs but also in other malignancies, such as lung cancer and melanoma³.

They are frequently high-grade tumors with morphological heterogeneity and/or ambiguity. At the molecular level, the majority of POLE-mutated tumors are microsatellite stable (65%), and TP53 mutations are present in 35% of cases. They also have mutations in PTEN (94%), FBXW7 (82%), ARID1A (76%), and PIK3CA (71%). Since patients with POLE-mutated tumors have an excellent prognosis, these women could benefit from conservative treatment. POLE ultramutated tumors are associated with an increase of CD8+ tumor-infiltrating lymphocytes, counterbalanced by overexpression of PDL-1 (an immune checkpoint protein) by the tumor cells, suggesting that these tumors might be excellent candidates for immune checkpoint inhibition (anti-PDL-1/PD1) ^2,4,6.

In spite of the great number of TCGA-related articles that appeared over the last 10 years, utility of TCGA has been limited to the rare cases of high-grade EECs with POLE. These patients have low risk of recurrence and can benefit from a de-escalating adjuvant treatment in early stage or from immune checkpoint inhibitors. The TCGA has also highlighted the importance of requesting immunohistochemistry for mismatch repair proteins in all ECs, particularly in endometrioid carcinomas, to identify patients with Lynch syndrome and patients who may benefit from immunotherapy. Knowledge about the other three molecular groups has not changed significantly.

EEC with MMRd represents approximately 35% of EEC cases, and has similar features to POLE carcinomas, but patients have older age at diagnosis and higher BMI. EECs with MMRd have a high mutational burden (18 x10^-6 mutations per Mb) and carry many neoantigens in the tumor cell surface. These neoantigens attract lymphocytes into the tumor, suggesting an immune-mediated role in the pathogenesis of these tumors. These tumors typically show extensive lymphocytic infiltration inside and around tumor cells. Microcystic elongated and fragmented (MELF) pattern of myometrial invasion and lymphovascular invasion are also associated with this molecular subtype.

TP53abn carcinomas account for 11% of EECs and have low mutation rate (2.7 x10^-6 mutations per Mb). Morphologically, these are high-grade (grade 3) EECs. These tumors have poor prognosis with recurrences and peritoneal dissemination, similar to serous carcinomas. Arising in older patients with low BMI, tumors are high-grade, histologically serous, endometrioid, and carcinosarcoma, and are characterized by aggressive histopathologic parameters (diffuse LVSI, lymph node metastasis, advanced stage).

NSMP tumors represent the majority of cases, related to higher BMI, and they are predominantly early-stage low-grade endometrioid carcinomas. This molecular subgroup is genomically relatively stable, MMR-proficient (Non-specific mutation profile; NSMP) and ccounts for 39% of EECs. Tumors have moderate number of mutations (2.9 x10^-6 mutations per Mb), mostly within the PI3K/Akt and Wnt signalling pathways. These patients have an intermediate prognosis.

Recently, CTNNB1 (beta-catenin 1) and L1 cell adhesion molecule (L1CAM) mutations have been associated with poor prognosis in EEC patients with a low degree of copy-number alterations. CTNNB1 mutation has been found to be associated with more distant recurrence [REFS]. In a separate study looking at low-grade early stage endometrioid EC, CTNNB1 mutation was also shown to be associated with poorer recurrence-free survival ^7,8. L1CAM is a membrane glycoprotein that plays a role in tumor cell migration. It is a strong predictor of decreased survival and is associated with adverse clinicopathological characteristics, namely > 50% myometrial invasion, LVSI, and lymph node involvement ^7,8. L1CAM may help to classify patients otherwise unclassifiable using the traditional EC molecular classification and is strongly associated with p53 ^7,8.

Conclusions

POLEmut endometrial carcinoma account for less than 10% of all ECs² and it is commonly associated with some of the worst prognostic factors, such as histotype (most commonly endometrioid type), high tumor grading, myometrial infiltration, lymphovascular invasion and low response to conventional treatments, as observed in preclinical data (chemotherapy and radiation), demostrating that conventional pathologic prognostic features are not so relevant in this subgroup: in fact, despite these unfavorable characteristics, POLEmut ECs present often at early stages (I-II) and show excellent prognosis with an indolent clinical course ^2,4.

Furthermore, POLEmut ECs frequently exhibit intense tumor-infiltrating lymphocytes and/or peri-tumoral lymphocytes, as MMRd ECs ⁴, suggesting a potential role of inflammation in the favorable outcome and a possible target for immunotherapies and, accordingly, the Food and Drug Administration has approved the anti-PD1 (pembrolizumab) for MMRd endometrial carcinomas with recurrence ⁶.

Further studies are requierd to define new pathogenic POLE exonuclease domain mutations in order to assess innovative therapies especially in young patients with endometrial carcinoma.

CONFLICTS OF INTEREST

The authors declare no conflict of interest.

FUNDING

None.

ETHICAL CONSIDERATION

The information contained in this manuscript complies with the journal’s ethical standards.

AUTHOR CONTRIBUTIONS

All authors gave their approval for pubbliclation of the final version of the manuscript .

Figures and tables

Figure 1.Endometrioid endometrial carcinoma with prominent architectural atypia (no solid pattern shown) stained in hematoxylin-eosin (10x).

Figure 2.Endometrioid endometrial carcinoma with evident cytologic atypia (round to oval nuclei, coarse chromatin, prominent nucleoli) stained in hematoxylin-eosin (40x).

Figure 3.Endometrioid endometrial carcinoma exhibiting heterogeneous p53 expression (10x).

References

1. Talhouk A, McConechy MK, Leung S. A clinically applicable molecular-based classification for endometrial cancers. Br J Cancer. 2015; 113:299-310. DOI
2. McAlpine JN, Chiu DS, Nout RA. Evaluation of treatment effects in patients with endometrial cancer and POLE mutations: An individual patient data meta-analysis. Cancer. 2021; 127:2409-2422. DOI
3. Levine D., The Cancer Genome Atlas Research Network. Integrated genomic characterization of endometrial carcinoma. Nature. 2013; 497:67-73. DOI
4. Léon-Castillo A. Update in the molecular classification of endometrial carcinoma. Int J Gynecol Cancer. 2023; 33:333-342. DOI
5. León-Castillo A, Britton H, McConechy MK. Interpretation of somatic POLE mutations in endometrial carcinoma. J Pathol. 2020; 250:323-335. DOI
6. Le DT, Uram JN, Wang H. PD-1 blockade in tumors with mismatch-repair deficiency. N Engl J Med. 2015; 372:2509-2520. DOI
7. Stelloo E, Nout RA, Osse EM. Improved Risk Assessment by Integrating Molecular and Clinicopathological Factors in Early-stage Endometrial Cancer-Combined Analysis of the PORTEC Cohorts. Clin Cancer Res. 2016; 15(22):4215-24. DOI
8. Laban M, El-Swaify ST, Ali SH. The Prediction of Recurrence in Low-Risk Endometrial Cancer: Is It Time for a Paradigm Shift in Adjuvant Therapy?. Reprod Sci. 2022; 29:1068-1085. DOI